In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Future RANs may look different in that a single UE may be served by multiple RBSs. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations. In some versions of a radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a controller node (such as a radio network controller (RNC) or a base station controller (BSC)) which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The number of radio access technologies available for uses such as cellular telephony and mobile broadband has grown rapidly in the later years. In the beginning of the 1990's there were only a few standards available, such as NMT, GSM and IS-95, used almost exclusively for voice telephony. Many additional radio access technologies (RATs) have been developed, such as W-CDMA, CDMA2000, EDGE, IEEE 802.16 and LTE, to mention a few. A multi-mode user terminal that can use several different RATs, such as the examples above, obtains improved coverage, e.g., so that users can use their terminals when traveling.
In this heterogeneous RAT environment, there is also a regulatory interest towards increasing flexibility in spectrum allocations with the advantage that the radio environment can be adapted to current usage patterns, and thus, limited radio resources can be more efficiently used. As a result, different RATs may be allocated to different frequencies in different locations, and these allocations may change over time.
FIG. 1 illustrates a heterogeneous RAT environment where a user equipment 12 may obtain service from multiple base stations (BSs) 14 that offer different radio access technologies (RATs). For example, one base station offers one RAT, DVB-H, on frequency band F1.1. Another base station offers two RATs, GSM on frequency band F2.1 and UMTS on frequency band F2.2. The remaining base station offers three RATs, WiFi on frequency band F3.1, GSM on frequency band F3.2, and UMTS on frequency band F3.3. As the question marks above the UE 12 indicate, one problem is to determine how to inform UEs about the specific RAT offerings and associated frequency bands.
One way to distribute information in radio environments with multiple RATs in a geographic region so that UEs can determine available RATs and how to connect to them is to use a Cognition enabling Pilot Channel (CPC). A wide-area, out-of-band CPC transmitter broadcasts, using a particular RAT and frequency already known to the UEs, information identifying which RATs (e.g., GSM, UMTS, W-CDMA, LTE, WiFi, and/or WiMax, etc.) are available and at what different frequencies in the different locations in a coverage area served by the CPC transmitter. The CPC transmitter may transmit using different frequencies than the frequencies used by the RATs and for that reason may be called an out-of-band wide area CPC transmitter.
One example way of dividing a wide-area radio access information coverage area up is in quadratic area elements like the mesh shown in FIG. 2. A wide area radio access information broadcast transmitter 18 transmits information for all of the mesh areas included in a service area 10. The wide area transmitter 18 transmits information for each mesh element “i” that includes location information of the mesh element, operator information, RAT information, frequency ranges associated with each RAT, and whether secondary usage is allowed and under what rules. Secondary usage refers to a situation where a UE is allowed to operate in a frequency band licensed to a certain RAT and/or operator but without connecting to that RAT and/or operator. Instead, the UE uses the frequency band for other communication purposes, e.g., for device-to-device communication with another party. Generally, secondary usage of frequency bands assumes that the UE (secondary user) somehow ensures that the quality of the primary service offered on the band is not degraded due to interference caused by the secondary usage.
With the introduction of more flexible and adaptable connection possibilities in UEs and the more dynamic spectrum arena that is likely to become reality in the future, the market for the introduction of local Dynamic Spectrum Access (DSA) hotspots becomes more attractive. A hotspot is a radio base station with small coverage and typically high capacity; one example is a WiFi hotspot at a coffee shop. A hotspot may, by using dynamic spectrum access mechanisms for example, obtain access to spectrum bands with more favorable propagation characteristics than provided by today's ISM band. Moreover, DSA hotspots could use discontiguous spectrum and aggregate a large bandwidth allowing for very high throughput.
To connect to a hotspot today, e.g., a WLAN hotspot, a UE needs to scan for hotspots in a limited frequency range. Even though the hotspot frequency band and the RAT used by the hotspot are already established, this UE scanning is still rather slow and power consuming. But if DSA is used, a UE wanting to connect to a DSA hotspot has even less information on where, in frequency, to scan for the hotspot or on what RAT is used by the DSA hotspot. The effect is a significant increase in the average scanning time and hence in connection time for users wanting to connect to the DSA hotspot resulting in lower user satisfaction, which is a significant drawback for the usefulness of hotspots.
To better attract users, it would be desirable for a DSA hotspot to efficiently announce its presence to nearby UEs and for UEs to be able to quickly connect to the hotspot without a time and energy consuming spectrum scanning.
The CPC could solve these problems by announcing to a UE on what frequencies it can connect to the hotspot and what RATs the hotspot is using. However, a wide-area CPC transmitter like that shown in FIG. 2 will have problems coping with many local DSA hotspots because of the large amount of information processing and transmission involved.
Furthermore, a wide-area CPC approach requires some degree of UE positioning meaning that a UE needs to know which CPC information is relevant for its present location. Since a hotspot typically has a small coverage area, that positioning has to be rather precise. Particularly for indoor use, which is where many hotspots are expected to be located, this could be a problem because GPS and similar positioning systems do not work indoors. Setting a high requirement on positioning precision may also be limiting to outdoor users since more complex UEs might be required (e.g., integrated GPS).
Another problem is that as local DSA hotspots change their operating frequencies and/or change the RAT(s) used to a dynamic local (in both time and space) frequency spectrum situation, it will be difficult to keep this information updated in a wide-area CPC transmitter.